The present invention is directed to a reactor, a structured packing, and a method for improving oxidation of hydrogen sulfide and/or polysulfides in liquid sulfur. More specifically, the reactor, the structured packing, and the method involve a catalyst for improving oxidation of the hydrogen sulfide and/or the polysulfides.
Generally, the Claus process is used to recover sulfur from hazardous waste gas streams containing hydrogen sulfide gas produced during refining of petroleum products and natural gas processing. The Claus process involves partially combusting hydrogen sulfide in air, oxygen, or oxygen-enriched air to produce sulfur dioxide. Sulfur dioxide then reacts with remaining hydrogen sulfide to produce sulfur. Sulfur is recovered from the Claus process in a liquid form. Handling of the liquid sulfur produced from the Claus process can be difficult due to the polysulfides and dissolved hydrogen sulfide gas present therein. The polysulfides degrade slowly, thereby producing toxic, odorous and highly flammable hydrogen sulfide gas. A large portion of the hydrogen sulfide gas is retained by liquid sulfur as a dissolved gas. A small portion of the hydrogen sulfide gas is released slowly into the environment. The gradual degradation of the polysulfides and the release of the dissolved hydrogen sulfide gas during storage and transportation involve substantial health, safety and environmental risks and have resulted in fires. The toxicity of hydrogen sulfide involves substantial safety risks.
Known processes have been developed to mitigate issues with the gradual release of hydrogen sulfide gas. In general, the processes involve accelerated decomposition of polysulfides and removal of dissolved hydrogen sulfide from liquid sulfur.
A known process for mitigating these issues is described in U.S. Pat. No. 5,632,967, which is hereby incorporated by reference in its entirety. The patent describes a first stream including liquid sulfur containing polysulfides and dissolved hydrogen sulfide and a second stream of oxygen-containing gas being contacted in a reactor (operated under pressure to increase oxygen partial pressure) packed with a mixing device. Specifically, the mixing device is submerged in the first stream including liquid sulfur and the second stream of oxygen-containing gas is bubbled into the first stream including liquid sulfur from the bottom of the reactor. The second stream of oxygen-containing gas oxidizes hydrogen sulfide and polysulfides present in the first stream including liquid sulfur to form sulfur and strip dissolved hydrogen sulfide from the liquid sulfur. The stripped hydrogen sulfide gas is removed from the top of the reactor along with any unused portions of the second stream of oxygen-containing gas. The stripped hydrogen sulfide gas and unused portions of the second stream of oxygen-containing gas may be recycled back to the reactor. The treated first stream including liquid sulfur includes less than about 10 parts per million by weight (ppmw) of combined polysulfides and dissolved hydrogen sulfide gas. The treated first stream including liquid sulfur is removed from the bottom of the reactor, stored as a liquid or solidified, then provided to end users.
Although the process described in U.S. Pat. No. 5,632,967 reduces the combined polysulfides and hydrogen sulfide amount in the liquid sulfur to less than about 10 ppmw, the process does not include decreasing the combined polysulfides and hydrogen sulfide content in the liquid sulfur to less than 5 ppmw. To meet increased environmental restrictions, a decreased combined polysulfides and hydrogen sulfide content in the liquid sulfur is desired. In addition, improved energy efficiency and operational costs are also desired. Furthermore, the process described in U.S. Pat. No. 5,632,967 involves a catalyst in a packed bed of spherical or pelletized catalyst. Catalytic oxidation of hydrogen sulfide and polysulfides in this patent mix the first stream and the second stream in the packed bed resulting in a high pressure drop and gradual crushing or disintegration of the spherical or pelletized catalyst, thereby contaminating the treated liquid sulfur stream and reducing marketable value of the treated liquid sulfur.
U.S. Pat. No. 6,149,887, which is hereby incorporated by reference in its entirety, discloses a method for removing hydrogen sulfide and hydrogen polysulfide compounds from liquid sulfur by stripping with a gas. U.S. Pat. No. 6,149,887 expressly suggests that use of a catalyst is disfavored. U.S. Pat. No. 6,149,887 suggests that introducing a catalyst to the liquid sulfur and, thereafter, stripping the catalyst from the sulfur can result in several drawbacks. This patent suggests that use of the catalyst may clog portions of the system and/or result in catalyst being present in the removed sulfur.
What is needed is a method and system for further decreasing combined polysulfides and hydrogen sulfide content in liquid sulfur, a method and system for decreasing combined polysulfides and hydrogen sulfide content in liquid sulfur having improved energy efficiency, and/or a method and system for decreasing combined polysulfides and hydrogen sulfide content in liquid sulfur having decreased operational costs.